1. Field of the Invention
The present invention relates to image forming apparatuses employing an electrophotography process, such as electrostatic copiers and electrostatic printers.
2. Description of the Related Art
Some image forming apparatuses employing an electrophotography process are configured to form an image by transferring toner images of a plurality of colors formed on photosensitive drums to an intermediate transfer member so as to be superimposed on one another and then transferring the superimposed images to a recording material.
Japanese Patent Laid-Open No. 2002-162833 discloses a technique for forming an elastic layer on an intermediate transfer member. Because of this elastic layer, the surface of the intermediate transfer member conforms to a recording material having unevenness. Thus, toner images can be uniformly transferred regardless of the unevenness of the recording material.
In this configuration, the intermediate transfer member needs to be cleaned to remove residual toner after images are formed thereon so that it can be used repeatedly. Therefore, for example, an edge of a cleaning blade made of an elastic material, such as rubber, is brought into contact with the intermediate transfer member to clean the intermediate transfer member.
However, in the above-described configuration, although the intermediate transfer member having an elastic layer can provide a good image by being deformed, it may cause color misregistration during color image formation or cleaning failure when such deformation remains.
In general, elastic members have a viscoelastic behavior. If such elastic members are kept pressed with a predetermined strain for a long time, stress relaxation occurs. Once the stress relaxation occurs, the time to recover from the deformation increases after the strain is released.
An intermediate transfer member having an elastic layer has a problem in that, when a recording material, such as a sheet, stops at a transfer portion in a sandwiched state due to conveyance failure, it tends to be deformed in an edge area of the recording material. In particular, this problem is noticeable with a thick recording material, such as cardboard, because the edge portion of the recording material significantly deforms the elastic intermediate transfer member.
When edge portions of a recording material in the conveying direction (side edges) are pressed against the intermediate transfer member for a long time, the intermediate transfer member is deformed at fixed positions in the longitudinal direction thereof (a direction perpendicular to the recording-material conveying direction). This may form a recess in the intermediate transfer member, which may cause local cleaning failure due to no pressure being applied at a cleaning portion.
Furthermore, when an edge portion of a recording material in the direction perpendicular to the conveying direction (a leading end or a trailing end) is pressed against the intermediate transfer member for a long time, a continuous recess extending in the longitudinal direction of the intermediate transfer member is formed. This may prevent a blade, serving as a cleaning member, from sufficiently conforming to the recess, causing cleaning failure. In addition, there may be a problem in that the cleaning blade is curled up when the edge of the cleaning blade in contact with the intermediate transfer member in the longitudinal direction is stuck in this recess. When the blade is curled up, the cleaning blade cannot exhibit its cleaning performance, causing cleaning failure.